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shares purchased without an initial sales charge and redeemed within 18 months of purchase for shares purchased on or after August 1, 2012, and within 24 months of purchase for shares purchased prior to August 1, 2012.On shares purchased without an initial sales charge and redeemed within 18 months of purchase for shares purchased on or after August 1, 2012, and within 24 months of purchase for shares purchased prior to August 1, 2012.Massachusetts Financial Services Company has agreed in writing to bear the fund's expenses, excluding interest, taxes, extraordinary expenses, brokerage and transaction costs, and investment-related expenses (such as interest and borrowing expenses incurred in connection with the fund's investment activity), such that "Total Annual Fund Operating Expenses" do not exceed 1.45% of the fund's average daily net assets annually for each of Class A and Class R3 shares, 2.20% of the fund's average daily net assets annually for each of Class B, Class C, and Class R1 shares, 1.20% of the fund's average daily net assets annually for each of Class I and Class R4 shares, 1.70% of the fund's average daily net assets annually for Class R2 shares, and 1.16% of the fund's average daily net assets annually for Class R5 shares. This written agreement will continue until modified by the fund's Board of Trustees, but such agreement will continue until at least June 30, 2015.MFS SERIES TRUST XIII485BPOSfalse00003563492013-02-282013-06-272013-06-282013-06-28MFS Diversified Income Fund Summary of Key InformationDIFAXDIFCXDIFIXDIFDXDIFEXDIFFXDIFGXDIFHXPortfolio Turnover<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These transaction costs, which are not reflected in &#8220;Annual Fund Operating Expenses&#8221; or in the &#8220;Example,&#8221; affect the fund&#8217;s performance.&#160; During the most recent fiscal year, the fund&#8217;s portfolio turnover rate was 64% of the average value of its portfolio.</font> </p>0.64Principal Risks<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The principal risks of investing in the fund are:</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Investment Selection and Allocation Risk:</font></b> <font size="2" style="font-size:10.0pt;">MFS&#8217; investment analysis, its selection of investments, and its assessment of the risk/return potential of asset classes may not produce the intended results and/or can lead to an investment focus that results in the fund underperforming other funds with similar investment strategies and/or underperforming the markets in which the fund invests.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Interest Rate Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;The price of a debt instrument falls when interest rates rise and rises when interest rates fall. Instruments with longer maturities, or that do not pay current interest, are more sensitive to interest rate changes.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Credit Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;The price of a debt instrument depends, in part, on the credit quality of the issuer, borrower, counterparty, or underlying collateral or assets and the terms of the instrument. The price of a debt instrument can decline in response to changes in the financial condition of the issuer, borrower, counterparty, or underlying collateral or assets, or changes in specific or general market, economic, industry, political, regulatory, geopolitical, and other conditions.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">Lower quality debt instruments (commonly referred to as &#8220;high yield securities&#8221; or &#8220;junk bonds&#8221;) can involve a substantially greater risk of default or can already be in default, and their values can decline significantly. Lower quality debt instruments are regarded as having predominantly speculative characteristics. Lower quality debt instruments tend to be more sensitive to adverse news about the issuer, or the market or economy in general, than higher quality debt instruments.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Foreign and Emerging Markets Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Exposure to foreign markets, especially emerging markets, through issuers or currencies can involve additional risks relating to market, economic, industry, political, regulatory, geopolitical, and other conditions. These factors can make foreign investments, especially those in emerging markets, more volatile and less liquid than U.S. investments. In addition, foreign markets can react differently to these conditions than the U.S. market. Emerging markets can have less developed markets, greater custody and operational risk, less developed legal, regulatory, and accounting systems, and greater political, social, and economic instability than developed markets.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Currency Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;The value of foreign currencies relative to the U.S. dollar fluctuates in response to market, economic, industry, political, regulatory, geopolitical, and other conditions, and a decline in the value of a foreign currency versus the U.S. dollar reduces the value in U.S. dollars of investments denominated in that foreign currency.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Prepayment/Extension Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Instruments subject to prepayment and/or extension can reduce the potential for gain for the instrument&#8217;s holders if the instrument is prepaid and increase the potential for loss if the maturity of the instrument is extended.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Inflation-Adjusted Debt Instruments Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Interest payments on inflation-adjusted debt instruments can be unpredictable and vary based on the level of inflation. If inflation is negative, principal and income can both decline.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Municipal Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;The price of a municipal instrument can be volatile and significantly affected by adverse tax or court rulings, legislative or political changes, changes in specific or general market and economic conditions, and the financial condition of municipal issuers and insurers. Because many municipal instruments are issued to finance similar projects, conditions in these industries can significantly affect the fund and the overall municipal market.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Stock Market/Company Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Stock markets are volatile and can decline significantly in response to issuer, market, economic, industry, political, regulatory, geopolitical, and other conditions, as well as to investor perceptions of these conditions. The price of an equity security can decrease significantly in response to these conditions, and these conditions can affect a single issuer or type of security, issuers within a broad market sector, industry or geographic region, or the market in general.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Value Company Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than the market in general.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Real Estate-Related Investment Risk:</font></b> <font size="2" style="font-size:10.0pt;">The risks of investing in real estate-related securities include certain risks associated with the direct ownership of real estate and the real estate industry in general. These include risks related to general, regional and local economic conditions; fluctuations in interest rates and property tax rates; shifts in zoning laws, environmental regulations and other governmental action; cash flow dependency; increased operating expenses; lack of availability of mortgage funds; losses due to natural disasters; overbuilding; losses due to casualty or condemnation; changes in property values and rental rates; and other factors.&#160; The securities of smaller real estate-related issuers can be more volatile and less liquid than securities of larger issuers and their issuers can have more limited financial resources.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Derivatives Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Derivatives can be highly volatile and involve risks in addition to the risks of the underlying indicator(s)&#160;on which the derivative is based. Gains or losses from derivatives can be substantially greater than the derivatives&#8217; original cost.&#160; Derivatives can involve leverage.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Leveraging Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Leverage involves investment exposure in an amount exceeding the initial investment. Leverage can cause increased volatility by magnifying gains or losses.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Counterparty and Third Party Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Transactions involving a counterparty or third party other than the issuer of the instrument are subject to the credit risk of the counterparty or third party, and to the counterparty&#8217;s or third party&#8217;s ability to perform in accordance with the terms of the transaction.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Liquidity Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;It may not be possible to sell certain investments, types of investments, and/or segments of the market at any particular time or at an acceptable price.</font> </p>As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund.An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.Fees and Expenses<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">This table describes the fees and expenses that you may pay when you buy and hold shares of the fund. 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Updated performance is available online at <b>mfs.com</b> or by calling 1-800-225-2606.</font> </p>Class A Bar Chart.0.0079-0.20410.30260.13920.05130.1319~ http://mfs.com/20130627/role/ScheduleAnnualTotalReturnsBarChart20005 column dei_LegalEntityAxis compact ck0000356349_S000012219Member column rr_ProspectusShareClassAxis compact ck0000356349_C000033358Member row primary compact * ~<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt;">The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund's shares. If these sales charges were included, they would reduce the returns shown.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-family: Times New Roman;"/> </p>highest quarterly return0.15832009-09-30lowest quarterly return-0.15172008-12-31The total return for the three-month period0.04042013-03-31<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The total return for the three-month period ended March&#160;31, 2013 was 4.04%. During the period(s)&#160;shown in the bar chart, the highest quarterly return was 15.83% (for the calendar quarter ended September&#160;30, 2009) and the lowest quarterly return was (15.17)% (for the calendar quarter ended December&#160;31, 2008).</font> </p>Performance Table. 0.11460.06280.0633C Shares Returns Before Taxes0.13470.07320.0739I Shares Returns Before Taxes0.12360.06290.0635R1 Shares Returns Before Taxes0.13020.06830.0689R2 Shares Returns Before Taxes0.13290.07100.0715R3 Shares Returns Before Taxes0.13470.07340.0740R4 Shares Returns Before Taxes0.13470.07320.0739R5 Shares Returns Before Taxes0.07810.06010.0631A Shares Returns Before Taxes0.06720.04530.0476A Shares Returns After Taxes on Distributions0.05210.04280.0451A Shares Returns After Taxes on Distributions and Sale of Fund Shares0.16000.01660.0394Index Comparisons (Reflects no deduction for fees, expenses or taxes) Standard & Poor's 500 Stock Index0.02270.05460.0605Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays U.S. Government/Mortgage Bond Index0.15780.10450.0937Index Comparisons (Reflects no deduction for fees, expenses or taxes) Barclays U.S. High-Yield Corporate Bond 2% Issuer Capped Index0.18540.10470.1046Index Comparisons (Reflects no deduction for fees, expenses or taxes) JPMorgan Emerging Markets Bond Index Global0.17770.05580.0497Index Comparisons (Reflects no deduction for fees, expenses or taxes) MSCI U.S. REIT Index (gross div)0.17510.00590.0266Index Comparisons (Reflects no deduction for fees, expenses or taxes) Russell 1000 Value Index2006-05-262006-05-262006-05-262006-05-262006-05-262006-05-262006-05-262006-05-262006-05-262006-05-262006-05-262006-05-262006-05-262006-05-26~ http://mfs.com/20130627/role/ScheduleAverageAnnualReturnsTransposed20006 column dei_LegalEntityAxis compact ck0000356349_S000012219Member column rr_PerformanceMeasureAxis compact * row primary compact * ~<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">Aft</font><font size="2" style="font-size:10.0pt;">er-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k)&#160;plans or individual retirement accounts. The after-tax returns are shown for only one of the fund&#8217;s classes of shares, and after-tax returns for the fund&#8217;s other classes of shares will vary from the returns shown.</font> </p> After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance and one or more other measures of performance for markets in which the fund may invest.The fund's past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.The after-tax returns are shown for only one of the fund's classes of shares, and after-tax returns for the fund's other classes of shares will vary from the returns shown.(Reflects no deduction for fees, expenses or taxes)The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund's shares. If these sales charges were included, they would reduce the returns shown.1-800-225-2606mfs.comYour actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.Average Annual Total Returns (for the Periods Ended December 31, 2012)Example<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods (unless otherwise indicated); your investment has a 5% return each year; and the fund&#8217;s operating expenses remain the same.</font> </p>581805104717412875799962159187579996215986268466103718757999621591364257341613111347601132986268466103778243422942~ http://mfs.com/20130627/role/ScheduleExpenseExampleTransposed20003 column dei_LegalEntityAxis compact ck0000356349_S000012219Member row primary compact * ~~ http://mfs.com/20130627/role/ScheduleExpenseExampleNoRedemptionTransposed20004 column dei_LegalEntityAxis compact ck0000356349_S000012219Member row primary compact * ~Although your actual costs will likely be higher or lower, under these assumptions your costs would be:Principal Investment Strategies<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS (Massachusetts Financial Services Company, the fund&#8217;s investment adviser) normally invests the fund&#8217;s assets primarily in a broad range of debt instruments and equity securities of U.S. and foreign issuers, including convertible securities, real estate-related investments, and emerging market securities. MFS may invest the fund&#8217;s assets in other mutual funds advised by MFS that invest in such instruments and securities instead of investing directly in such instruments and securities.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS allocates the fund&#8217;s assets across these categories based on its interpretation of economic and money market conditions, fiscal and monetary policy and asset class and/or security values. These allocations may vary from time to time.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS focuses the fund&#8217;s debt investments on U.S. Government securities, less than investment grade quality debt instruments (lower quality debt instruments), and debt instruments of emerging market issuers. Of the fund&#8217;s investments in debt instruments, MFS may invest up to 100% of these investments directly or indirectly in lower quality debt instruments.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">For the equity portion of the fund, MFS focuses on investing the fund&#8217;s assets in dividend-paying stocks and/or in the stocks of companies it believes are undervalued compared to their perceived worth (value companies). While MFS may invest the equity portion of the fund&#8217;s assets in companies of any size, MFS generally focuses on companies with large capitalizations.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">For the real estate-related portion of the fund, MFS invests the fund&#8217;s assets in real estate investment trusts (REITs) and other companies principally engaged in the real estate industry. MFS generally focuses the fund&#8217;s investments in equity REITs, but may also invest in mortgage REITs and other real estate-related investments.&#160; Issuers of real estate-related investments tend to be small- to medium-sized.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives, MFS expects to use derivatives primarily to increase or decrease exposure to a particular market, segment of the market, or security, to increase or decrease interest rate or currency exposure, or as alternatives to direct investments. Derivatives include futures, forward contracts, options, structured securities, inverse floating rate instruments, and swaps.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS uses a bottom-up investment approach to buying and selling investments for the fund. Investments are selected based on fundamental analysis of individual issuers and instruments and quantitative models that systematically evaluate issuers and instruments. In structuring the fund, MFS may also consider top-down factors.</font> </p>Investment Objective<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The fund&#8217;s investment objective is to seek total return with an emphasis on current income, but also considering capital appreciation.</font> </p>MFS Global Real Estate Fund Summary of Key InformationMGLAXMGLIXMGLRXPortfolio Turnover<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These transaction costs, which are not reflected in &#8220;Annual Fund Operating Expenses&#8221; or in the &#8220;Example,&#8221; affect the fund&#8217;s performance.&#160; During the most recent fiscal year, the fund&#8217;s portfolio turnover rate was 46% of the average value of its portfolio.</font> </p>0.46Principal Risks<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The principal risks of investing in the fund are:</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Real Estate-Related Investment Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;The fund&#8217;s performance will be closely tied to the performance of real estate-related investments and as a result, can be more volatile than the performance of more broadly-diversified funds. The risks of investing in real estate-related investments include certain risks associated with the direct ownership of real estate and the real estate industry in general. These include risks related to general, regional and local economic conditions; fluctuations in interest rates and property tax rates; shifts in zoning laws, environmental regulations and other governmental action; cash flow dependency; increased operating expenses; lack of availability of mortgage funds; losses due to natural disasters; overbuilding; losses due to casualty or condemnation; changes in property values and rental rates; and other factors.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Small to Medium Cap Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;The securities of small and medium-sized real estate-related issuers can be more volatile and less liquid than securities of larger issuers and their issuers can have more limited financial resources.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Stock Market/Company Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Stock markets are volatile and can decline significantly in response to issuer, market, economic, industry, political, regulatory, geopolitical, and other conditions, as well as to investor perceptions of these conditions. The price of an equity security can decrease significantly in response to these conditions, and these conditions can affect a single issuer or type of security, issuers within a broad market sector, industry or geographic region, or the market in general.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Foreign and Emerging Markets Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Exposure to foreign markets, especially emerging markets, through issuers or currencies can involve additional risks relating to market, economic, industry, political, regulatory, geopolitical, and other conditions. These factors can make foreign investments, especially those in emerging markets, more volatile and less liquid than U.S. investments. In addition, foreign markets can react differently to these conditions than the U.S. market. Emerging markets can have less developed markets, greater custody and operational risk, less developed legal, regulatory, and accounting systems, and greater political, social, and economic instability than developed markets.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Currency Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;The value of foreign currencies relative to the U.S. dollar fluctuates in response to market, economic, industry, political, regulatory, geopolitical, and other conditions, and a decline in the value of a foreign currency versus the U.S. dollar reduces the value in U.S. dollars of investments denominated in that foreign currency.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Geographic Concentration Risk:</font></b> <font size="2" style="font-size:10.0pt;">The fund&#8217;s performance could be closely tied to the market, currency, economic, political, regulatory, geopolitical, and other conditions in the countries or regions in which the fund invests and could be more volatile than the performance of more geographically-diversified funds.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Investment Selection Risk:</font></b> <font size="2" style="font-size:10.0pt;">MFS&#8217; investment analysis and its selection of investments may not produce the intended results and/or can lead to an investment focus that results in the fund underperforming other funds with similar investment strategies and/or underperforming the markets in which the fund invests.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Liquidity Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;It may not be possible to sell certain investments, types of investments, and/or segments of the market at any particular time or at an acceptable price.</font> </p>As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund.An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.Fees and Expenses<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">This table describes the fees and expenses that you may pay when you buy and hold shares of the fund. The annual fund operating expenses for Class B, Class C, Class R1, Class R2, Class R3, and Class R4 shares are based on estimated &#8220;Other Expenses&#8221; for the current fiscal year expressed as a percentage of the fund&#8217;s estimated average net assets during the period.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">You may qualify for sales charge reductions if you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS Funds. More information about these and other waivers and reductions is available from your financial intermediary and in &#8220;Sales Charges and Waivers or Reductions&#8221; on page 8 of the fund&#8217;s prospectus and &#8220;Waivers of Sales Charges&#8221; on page I-13 of the fund&#8217;s statement of additional information Part I.</font> </p>0.05750.00000.00000.00000.00000.00000.00000.00000.00000.01000.04000.01000.00000.00000.00000.00000.00000.00000.00900.00900.00900.00900.00900.00900.00900.00900.00900.00250.01000.01000.00000.01000.00500.00250.00000.00000.00080.00080.00080.00080.00080.00080.00080.00080.00080.01230.01980.01980.00980.01980.01480.01230.00980.0098~ http://mfs.com/20130627/role/ScheduleShareholderFees20009 column dei_LegalEntityAxis compact ck0000356349_S000024971Member row primary compact * ~~ http://mfs.com/20130627/role/ScheduleAnnualFundOperatingExpenses20010 column dei_LegalEntityAxis compact ck0000356349_S000024971Member row primary compact * ~You may qualify for sales charge reductions if you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS Funds.Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)50000On shares purchased without an initial sales charge and redeemed within 18 months of purchase for shares purchased on or after August 1, 2012, and within 24 months of purchase for shares purchased prior to August 1, 2012.Shareholder Fees (fees paid directly from your investment)Performance Information<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund&#8217;s performance over time and how the fund&#8217;s performance over time compares with that of a broad measure of market performance.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The fund&#8217;s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at <b>mfs.com</b> or by calling 1-800-225-2606.</font> </p>Class A Bar Chart.0.1529-0.07220.2949~ http://mfs.com/20130627/role/ScheduleAnnualTotalReturnsBarChart20013 column dei_LegalEntityAxis compact ck0000356349_S000024971Member column rr_ProspectusShareClassAxis compact ck0000356349_C000074269Member row primary compact * ~<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt;">The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund's shares. If these sales charges were included, they would reduce the returns shown.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-family: Times New Roman;"/> </p>highest quarterly return0.18702010-09-30lowest quarterly return-0.18052011-09-30The total return for the three-month period0.05592013-03-31<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The total return for the three-month period ended March 31, 2013 was 5.59%. During the period(s) shown in the bar chart, the highest quarterly return was 18.70% (for the calendar quarter ended September 30, 2010) and the lowest quarterly return was (18.05)% (for the calendar quarter ended September 30, 2011).</font> </p>Performance Table. 0.24400.2850B Shares Returns Before Taxes 0.27400.2889C Shares Returns Before Taxes 0.29680.3018I Shares Returns Before Taxes 0.28400.2889R1 Shares Returns Before Taxes 0.29040.2953R2 Shares Returns Before Taxes 0.29360.2985R3 Shares Returns Before Taxes 0.29680.3018R4 Shares Returns Before Taxes 0.29680.3018R5 Shares Returns Before Taxes 0.22040.2787A Shares Returns Before Taxes 0.19760.2205A Shares Returns After Taxes on Distributions 0.14890.2104A Shares Returns After Taxes on Distributions and Sale of Fund Shares 0.28650.3227Index Comparison (Reflects no deduction for fees, expenses or taxes) FTSE EPRA/NAREIT Developed Real Estate Index2009-03-112009-03-112009-03-112009-03-112009-03-112009-03-112009-03-112009-03-112009-03-112009-03-11~ http://mfs.com/20130627/role/ScheduleAverageAnnualReturnsTransposed20014 column dei_LegalEntityAxis compact ck0000356349_S000024971Member column rr_PerformanceMeasureAxis compact * row primary compact * ~<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">Aft</font><font size="2" style="font-size:10.0pt;">er-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts. The after-tax returns are shown for only one of the fund&#8217;s classes of shares, and after-tax returns for the fund&#8217;s other classes of shares will vary from the returns shown.</font> </p> After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.The fund's past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.The after-tax returns are shown for only one of the fund's classes of shares, and after-tax returns for the fund's other classes of shares will vary from the returns shown.(Reflects no deduction for fees, expenses or taxes)The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund's shares. If these sales charges were included, they would reduce the returns shown.1-800-225-2606mfs.comAverage Annual Total Returns (for the Periods Ended December 31, 2012)Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.Example<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods (unless otherwise indicated); your investment has a 5% return each year; and the fund&#8217;s operating expenses remain the same.</font> </p>69394312121978601921126821132016211068211330162110682306201621106823061003125421201201621106823061514688081768125390676148910031254212011003125421201~ http://mfs.com/20130627/role/ScheduleExpenseExampleTransposed20011 column dei_LegalEntityAxis compact ck0000356349_S000024971Member row primary compact * ~~ http://mfs.com/20130627/role/ScheduleExpenseExampleNoRedemptionTransposed20012 column dei_LegalEntityAxis compact ck0000356349_S000024971Member row primary compact * ~Although your actual costs will likely be higher or lower, under these assumptions your costs would be:Principal Investment Strategies<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS (Massachusetts Financial Services Company, the fund&#8217;s investment adviser) normally invests at least 80% of the fund&#8217;s net assets in U.S. and foreign real estate-related investments.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS normally invests the fund&#8217;s assets primarily in equity securities.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS generally focuses the fund&#8217;s investments in equity real estate investment trusts (&#8220;REITs&#8221;) as well as similar entities formed under the laws of non-U.S. countries, but may also invest in mortgage REITs, hybrid REITs and other U.S. and foreign real estate-related investments, including emerging market real estate-related investments.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS may invest the fund&#8217;s assets in real estate-related investments of any size.&#160; However, issuers of real estate-related investments tend to be small-to-medium-sized.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS typically allocates the fund&#8217;s investments across various geographic areas, REIT managers and property types, but may from time to time focus the fund&#8217;s investments in any one or a few of these areas.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS may invest a large percentage of the fund&#8217;s assets in issuers in a single country, a small number of countries, or a particular geographic region.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS selects investments by analyzing the fundamental and relative values of potential investments.</font> </p>MFS (Massachusetts Financial Services Company, the fund's investment adviser) normally invests at least 80% of the fund's net assets in U.S. and foreign real estate-related investments.Investment Objective<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The fund&#8217;s investment objective is to seek total return.</font> </p>MFS Government Securities Fund Summary of Key InformationMGSIXMFGSXMFGJXMFGBXMFGDXMFGGXMGVSXMFGHXMFGKXPortfolio Turnover<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These transaction costs, which are not reflected in &#8220;Annual Fund Operating Expenses&#8221; or in the &#8220;Example,&#8221; affect the fund&#8217;s performance.&#160; During the most recent fiscal year, the fund&#8217;s portfolio turnover rate was 81% of the average value of its portfolio.</font> </p>0.81Principal Risks<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The principal risks of investing in the fund are:</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Interest Rate Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;The price of a debt instrument falls when interest rates rise and rises when interest rates fall. Instruments with longer maturities, or that do not pay current interest, are more sensitive to interest rate changes.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Credit Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;The price of a debt instrument depends, in part, on the credit quality of the issuer, borrower, counterparty, or underlying collateral or assets and the terms of the instrument. The price of a debt instrument can decline in response to changes in the financial condition of the issuer, borrower, counterparty, or underlying collateral or assets, or changes in specific or general market, economic, industry, political, regulatory, geopolitical, and other conditions.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">U.S. Government securities not supported as to the payment of principal or interest by the U.S. Treasury are subject to greater credit risk than are U.S. Government securities supported by the U.S. Treasury.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Issuer Focus Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;The fund&#8217;s performance could be more volatile than the performance of more diversified funds.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Prepayment/Extension Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Instruments subject to prepayment and/or extension can reduce the potential for gain for the instrument&#8217;s holders if the instrument is prepaid and increase the potential for loss if the maturity of the instrument is extended.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Inflation-Adjusted Debt Instruments Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Interest payments on inflation-adjusted debt instruments can be unpredictable and vary based on the level of inflation. If inflation is negative, principal and income can both decline.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Derivatives Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Derivatives can be highly volatile and involve risks in addition to the risks of the underlying indicator(s)&#160;on which the derivative is based. Gains or losses from derivatives can be substantially greater than the derivatives&#8217; original cost.&#160; Derivatives can involve leverage.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Leveraging Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Leverage involves investment exposure in an amount exceeding the initial investment. Leverage can cause increased volatility by magnifying gains or losses.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Investment Selection Risk:</font></b> <font size="2" style="font-size:10.0pt;">MFS&#8217; investment analysis and its selection of investments may not produce the intended results and/or can lead to an investment focus that results in the fund underperforming other funds with similar investment strategies and/or underperforming the markets in which the fund invests.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Counterparty and Third Party Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Transactions involving a counterparty or third party other than the issuer of the instrument are subject to the credit risk of the counterparty or third party, and to the counterparty&#8217;s or third party&#8217;s ability to perform in accordance with the terms of the transaction.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Liquidity Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;It may not be possible to sell certain investments, types of investments, and/or segments of the market at any particular time or at an acceptable price.</font> </p>As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund.An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.Fees and Expenses<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">This table describes the fees and expenses that you may pay when you buy and hold shares of the fund. &#160;You may qualify for sales charge reductions if you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS Funds. More information about these and other waivers and reductions is available from your financial intermediary and in &#8220;Sales Charges and Waivers or Reductions&#8221; on page&#160;8 of the fund&#8217;s prospectus and &#8220;Waivers of Sales Charges&#8221; on page&#160;I-14 of the fund&#8217;s statement of additional information Part&#160;I.</font> </p>0.04750.00000.00000.00000.00000.00000.00000.00000.00000.01000.04000.01000.00000.00000.00000.00000.00000.00000.00400.00400.00400.00400.00400.00400.00400.00400.00400.00250.01000.01000.00000.01000.00500.00250.00000.00000.00200.00200.00200.00200.00200.00200.00200.00200.00100.00850.01600.01600.00600.01600.01100.00850.00600.0050~ http://mfs.com/20130627/role/ScheduleShareholderFees20017 column dei_LegalEntityAxis compact ck0000356349_S000000693Member row primary compact * ~~ http://mfs.com/20130627/role/ScheduleAnnualFundOperatingExpenses20018 column dei_LegalEntityAxis compact ck0000356349_S000000693Member row primary compact * ~You may qualify for sales charge reductions if you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS Funds.Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)50000On shares purchased without an initial sales charge and redeemed within 18 months of purchase for shares purchased on or after August 1, 2012, and within 24 months of purchase for shares purchased prior to August 1, 2012.Shareholder Fees (fees paid directly from your investment)Performance Information<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund&#8217;s performance over time and how the fund&#8217;s performance over time compares with that of a broad measure of market performance.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The fund&#8217;s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at <b>mfs.com</b> or by calling 1-800-225-2606.</font> </p>Class A Bar Chart.0.01540.03300.02170.03600.07070.08510.04230.04590.07190.0208~ http://mfs.com/20130627/role/ScheduleAnnualTotalReturnsBarChart20021 column dei_LegalEntityAxis compact ck0000356349_S000000693Member column rr_ProspectusShareClassAxis compact ck0000356349_C000002007Member row primary compact * ~<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt;">The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund's shares. If these sales charges were included, they would reduce the returns shown.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="3" style="font-family: Times New Roman;"/> </p>highest quarterly return0.05292008-12-31lowest quarterly return-0.02232004-06-30The total return for the three-month period-0.00302013-03-31<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The total return for the three-month period ended March&#160;31, 2013 was (0.30)%. During the period(s)&#160;shown in the bar chart, the highest quarterly return was 5.29% (for the calendar quarter ended December&#160;31, 2008) and the lowest quarterly return was (2.23)% (for the calendar quarter ended June&#160;30, 2004).</font> </p>Performance Table. -0.02640.04180.0380B Shares Returns Before Taxes 0.00330.04490.0363C Shares Returns Before Taxes 0.02340.05560.0468I Shares Returns Before Taxes 0.01320.04510.0355R1 Shares Returns Before Taxes 0.01830.05040.0405R2 Shares Returns Before Taxes 0.02080.05300.0433R3 Shares Returns Before Taxes 0.02340.05560.0462R4 Shares Returns Before Taxes 0.02270.05540.0468R5 Shares Returns Before Taxes -0.02760.04280.0390A Shares Returns Before Taxes -0.03710.03030.0251A Shares Returns After Taxes on Distributions -0.01730.02920.0250A Shares Returns After Taxes on Distributions and Sale of Fund Shares 0.02270.05460.0487Index Comparison (Reflects no deduction for fees, expenses or taxes) Barclays U.S. Government/Mortgage Bond Index~ http://mfs.com/20130627/role/ScheduleAverageAnnualReturnsTransposed20022 column dei_LegalEntityAxis compact ck0000356349_S000000693Member column rr_PerformanceMeasureAxis compact * row primary compact * ~<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">Aft</font><font size="2" style="font-size:10.0pt;">er-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k)&#160;plans or individual retirement accounts. The after-tax returns are shown for only one of the fund&#8217;s classes of shares, and after-tax returns for the fund&#8217;s other classes of shares will vary from the returns shown.</font> </p> After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing changes in the fund's performance over time and how the fund's performance over time compares with that of a broad measure of market performance.The fund's past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.The after-tax returns are shown for only one of the fund's classes of shares, and after-tax returns for the fund's other classes of shares will vary from the returns shown.(Reflects no deduction for fees, expenses or taxes)The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund's shares. If these sales charges were included, they would reduce the returns shown.1-800-225-2606mfs.comAverage Annual Total Returns (for the Periods Ended December 31, 2012)Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.Example<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods (unless otherwise indicated); your investment has a 5% return each year; and the fund&#8217;s operating expenses remain the same.</font> </p>55873392414745638051071169916350587116992635058711900163505871190061192335750163505871190011235060613408727147110496119233575051160280628~ http://mfs.com/20130627/role/ScheduleExpenseExampleTransposed20019 column dei_LegalEntityAxis compact ck0000356349_S000000693Member row primary compact * ~~ http://mfs.com/20130627/role/ScheduleExpenseExampleNoRedemptionTransposed20020 column dei_LegalEntityAxis compact ck0000356349_S000000693Member row primary compact * ~Although your actual costs will likely be higher or lower, under these assumptions your costs would be:Principal Investment Strategies<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS (Massachusetts Financial Services Company, the fund&#8217;s investment adviser) normally invests at least 80% of the fund&#8217;s net assets in U.S. Government securities.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS generally invests substantially all of the fund&#8217;s assets in investment grade debt instruments.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS may invest a relatively large percentage of the fund&#8217;s assets in a single issuer or a small number of issuers.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">While MFS may use derivatives for any investment purpose, to the extent MFS uses derivatives, MFS expects to use derivatives primarily to increase or decrease exposure to a particular market, segment of the market, or security, to increase or decrease interest rate exposure, or as alternatives to direct investments. Derivatives include futures, forward contracts, options, structured securities, inverse floating rate instruments, and swaps.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS uses a bottom-up investment approach to buying and selling investments for the fund. Investments are selected primarily based on fundamental analysis of individual instruments and their issuers. Quantitative models that systematically evaluate instruments may also be considered. In structuring the fund, MFS may also consider top-down factors.</font> </p>Investment Objective<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The fund&#8217;s investment objective is to seek total return with an emphasis on current income, but also considering capital appreciation.</font> </p>MFS New Discovery Value Fund Summary of Key InformationNDVAXNDVBXNDVCXNDVIXNDVRXNDVSXNDVTXNDVUXNDVVXPortfolio Turnover<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The fund pays transaction costs, such as commissions, when it buys and sells securities (or &#8220;turns over&#8221; its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These transaction costs, which are not reflected in &#8220;Annual Fund Operating Expenses&#8221; or in the &#8220;Example,&#8221; affect the fund&#8217;s performance.&#160; During the most recent fiscal year, the fund&#8217;s portfolio turnover rate was 67% of the average value of its portfolio.</font> </p>0.67Principal Risks<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund. An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The principal risks of investing in the fund are:</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Stock Market/Company Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Stock markets are volatile and can decline significantly in response to issuer, market, economic, industry, political, regulatory, geopolitical, and other conditions, as well as to investor perceptions of these conditions. The price of an equity security can decrease significantly in response to these conditions, and these conditions can affect a single issuer or type of security, issuers within a broad market sector, industry or geographic region, or the market in general.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Value Company Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;The stocks of value companies can continue to be undervalued for long periods of time and not realize their expected value and can be more volatile than the market in general.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Small Cap Risk:</font></b><font size="2" style="font-size:10.0pt;">&#160; The stocks of small cap companies can be more volatile than stocks of larger companies.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Foreign Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;Exposure to foreign markets through issuers or currencies can involve additional risks relating to market, economic, industry, political, regulatory, geopolitical, and other conditions. These factors can make foreign investments, especially those in emerging markets, more volatile and less liquid than U.S. investments. In addition, foreign markets can react differently to these conditions than the U.S. market.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Real Estate Investment Trust Risk:</font></b> <font size="2" style="font-size:10.0pt;">The risks of investing in REITs include certain risks associated with the direct ownership of real estate and the real estate industry in general. These include risks related to general, regional and local economic conditions; fluctuations in interest rates and property tax rates; shifts in zoning laws, environmental regulations and other governmental action; cash flow dependency; increased operating expenses; lack of availability of mortgage funds; losses due to natural disasters; overbuilding; losses due to casualty or condemnation; changes in property values and rental rates; and other factors.&#160; The securities of smaller real estate-related issuers can be more volatile and less liquid than securities of larger issuers and their issuers can have more limited financial resources.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Investment Selection Risk:</font></b> <font size="2" style="font-size:10.0pt;">MFS&#8217; investment analysis and its selection of investments may not produce the intended results and/or can lead to an investment focus that results in the fund underperforming other funds with similar investment strategies and/or underperforming the markets in which the fund invests.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <b><font size="2" style="font-size:10.0pt;font-weight:bold; font-family: Times New Roman;">Liquidity Risk:</font></b> <font size="2" style="font-size:10.0pt;">&#160;It may not be possible to sell certain investments, types of investments, and/or segments of the market at any particular time or at an acceptable price.</font> </p>As with any mutual fund, the fund may not achieve its objective and/or you could lose money on your investment in the fund.An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other governmental agency.Fees and Expenses<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">This table describes the fees and expenses that you may pay when you buy and hold shares of the fund. Expenses have been adjusted to reflect current fee arrangements.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">You may qualify for sales charge reductions if you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS Funds. More information about these and other waivers and reductions is available from your financial intermediary and in &#8220;Sales Charges and Waivers or Reductions&#8221; on page&#160;7 of the fund&#8217;s prospectus and &#8220;Waivers of Sales Charges&#8221; on page&#160;I-15 of the fund&#8217;s statement of additional information Part&#160;I.</font> </p>0.05750.00000.00000.00000.00000.00000.00000.00000.00000.01000.04000.01000.00000.00000.00000.00000.00000.00000.00900.00900.00900.00900.00900.00900.00900.00900.00900.00250.01000.01000.00000.01000.00500.00250.00000.00000.00470.00470.00470.00470.00470.00470.00470.00470.00410.01620.02370.02370.01370.02370.01870.01620.01370.0131-0.0017-0.0017-0.0017-0.0017-0.0017-0.0017-0.0017-0.0017-0.00150.01450.02200.02200.01200.02200.01700.01450.01200.0116~ http://mfs.com/20130627/role/ScheduleShareholderFees20025 column dei_LegalEntityAxis compact ck0000356349_S000032712Member row primary compact * ~~ http://mfs.com/20130627/role/ScheduleAnnualFundOperatingExpenses20026 column dei_LegalEntityAxis compact ck0000356349_S000032712Member row primary compact * ~2015-06-30Expenses have been adjusted to reflect current fee arrangements.You may qualify for sales charge reductions if you and certain members of your family invest, or agree to invest in the future, at least $50,000 in MFS Funds.Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)50000On shares purchased without an initial sales charge and redeemed within 18 months of purchase for shares purchased on or after August 1, 2012, and within 24 months of purchase for shares purchased prior to August 1, 2012.Shareholder Fees (fees paid directly from your investment)Performance Information<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing how the fund&#8217;s performance over time compares with that of a broad measure of market performance.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The fund&#8217;s past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future. Updated performance is available online at <b>mfs.com</b> or by calling 1-800-225-2606.</font> </p>Class A Bar Chart.0.2015~ http://mfs.com/20130627/role/ScheduleAnnualTotalReturnsBarChart20029 column dei_LegalEntityAxis compact ck0000356349_S000032712Member column rr_ProspectusShareClassAxis compact ck0000356349_C000100956Member row primary compact * ~<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt;">The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund's shares. If these sales charges were included, they would reduce the returns shown.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-family: Times New Roman;"/> </p>highest quarterly return0.14862012-03-31lowest quarterly return-0.02762012-06-30The total return for the three-month period0.12702013-03-31<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The total return for the three-month period ended March&#160;31, 2013 was 12.70%. During the period(s)&#160;shown in the bar chart, the highest quarterly return was 14.86% (for the calendar quarter ended March&#160;31, 2012) and the lowest quarterly return was (2.76)% (for the calendar quarter ended June&#160;30, 2012).</font> </p>Performance Table. 0.15190.0367B Shares Returns Before Taxes 0.18290.0611C Shares Returns Before Taxes 0.20490.0717I Shares Returns Before Taxes 0.19210.0611R1 Shares Returns Before Taxes 0.19940.0666R2 Shares Returns Before Taxes 0.20210.0691R3 Shares Returns Before Taxes 0.20490.0717R4 Shares Returns Before Taxes 0.20510.0718R5 Shares Returns Before Taxes 0.13240.0305A Shares Returns Before Taxes 0.11050.0176A Shares Returns After Taxes on Distributions 0.08800.0192A Shares Returns After Taxes on Distributions and Sale of Fund Shares 0.18050.0512Index Comparison (Reflects no deduction for fees, expenses or taxes) Russell 2000 Value Index2011-05-262011-05-262011-05-262011-05-262011-05-262011-05-262011-05-262011-05-262011-05-262011-05-26~ http://mfs.com/20130627/role/ScheduleAverageAnnualReturnsTransposed20030 column dei_LegalEntityAxis compact ck0000356349_S000032712Member column rr_PerformanceMeasureAxis compact * row primary compact * ~<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">Aft</font><font size="2" style="font-size:10.0pt;">er-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes. Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k)&#160;plans or individual retirement accounts. The after-tax returns are shown for only one of the fund&#8217;s classes of shares, and after-tax returns for the fund&#8217;s other classes of shares will vary from the returns shown.</font> </p> After-tax returns are calculated using the historical highest individual federal marginal income tax rates and do not reflect the impact of state and local taxes.The bar chart and performance table below are intended to provide some indication of the risks of investing in the fund by showing how the fund's performance over time compares with that of a broad measure of market performance.The fund's past performance (before and after taxes) does not necessarily indicate how the fund will perform in the future.The after-tax returns are shown for only one of the fund's classes of shares, and after-tax returns for the fund's other classes of shares will vary from the returns shown.(Reflects no deduction for fees, expenses or taxes)The bar chart does not take into account any sales charges (loads) that you may be required to pay upon purchase or redemption of the fund's shares. If these sales charges were included, they would reduce the returns shown.1-800-225-2606mfs.comAverage Annual Total Returns (for the Periods Ended December 31, 2012)Your actual after-tax returns will depend on your own tax situation, and may differ from those shown. The after-tax returns shown are not relevant to investors who hold their shares through tax-deferred arrangements, such as 401(k) plans or individual retirement accounts.Example<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The example assumes that: you invest $10,000 in the fund for the time periods indicated and you redeem your shares at the end of the time periods (unless otherwise indicated); your investment has a 5% return each year; and the fund&#8217;s operating expenses remain the same.</font> </p>7141025137523596231006143424922237061234249232370612342679223706123426791224007171616223706123426791735549792162148477848189212240071716161183856891552~ http://mfs.com/20130627/role/ScheduleExpenseExampleTransposed20027 column dei_LegalEntityAxis compact ck0000356349_S000032712Member row primary compact * ~~ http://mfs.com/20130627/role/ScheduleExpenseExampleNoRedemptionTransposed20028 column dei_LegalEntityAxis compact ck0000356349_S000032712Member row primary compact * ~Although your actual costs will likely be higher or lower, under these assumptions your costs would be:Principal Investment Strategies<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS (Massachusetts Financial Services Company, the fund&#8217;s investment adviser) normally invests the fund&#8217;s assets primarily in equity securities. Equity securities include common stocks, preferred stocks, securities convertible into stocks, equity interests in real estate investment trusts (REITs), and depositary receipts for such securities.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS focuses on investing the fund&#8217;s assets in the stocks of companies it believes are undervalued compared to their perceived worth (value companies).</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">While MFS may invest the fund&#8217;s assets in companies of any size, MFS generally focuses on companies with small capitalizations.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS may invest the fund&#8217;s assets in foreign securities.</font> </p> <br/><p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">MFS uses a bottom-up investment approach to buying and selling investments for the fund. Investments are selected primarily based on fundamental analysis of individual issuers. Quantitative models that systematically evaluate issuers may also be considered.</font> </p>Investment Objective<p style="margin:0in 0in .0001pt;"> <font size="2" style="font-size:10.0pt; font-family: Times New Roman;">The fund&#8217;s investment objective is to seek capital appreciation.</font> </p>